The Big Bang Theory exec producer Chuck Lorre is fond of saying that the show isn’t Lost – there’s no grand plan in place building to a revelatory event at the end of the season. Be that as it may, the fifth season of Big Bang has been leading directly to tonight’s finale: the wedding of Howard Wolowitz (Simon Helberg) and Bernadette Rostenkowski (Melissa Rauch), and Howard’s on-again, off-again, on-again mission to the International Space Station. Both of those events converge tonight, and the question is: Will the wedding happen? Will Howard go through with the mission? Will there be a massive cliffhanger like last season’s ohmigod, did Penny and Raj-just get horizontal?! bombshell? We rang up Big Bang EP Bill Prady to grill him for answers:

ENTERTAINMENT WEEKLY: How have you felt about season 5?BILL PRADY: My favorite so far, I would have to say. We started out in a weird, cool place, because we’d boxed ourselves into a corner at the end of season 4, as we often do. We found a way out in I think one of the best episodes we’ve done that started the season. And my God, this season has included Steven Hawking and Leonard Nimoy and the crazy bird that Sheldon loves, and Wolowitz’s NASA story, and planning for a wedding. There’s been so much in this season that’s been so fun.

You really expanded your cast this season – Bernadette and Amy started as series regulars in season 4, but they really established themselves fully this year.
I’ve been asked about this a couple of times, and as I’ve said, it was not by design. We didn’t say, “Let’s expand the cast! How are we going to do it?” We found two actresses and two characters that we love, and it was a week-to-week thing. “Let’s see her again. Let’s see her again. And, you know what, I think we’re just going to see her a lot.” That’s a wonderful expansion, not part of some plan.

So talk to me about the finale. Howard is going into space?
That’s a big part of what’s going on in there. Howard is in Kazakhstan getting ready to head up into space. He will recall the events that got him there. The episode’s told in flashback.

Is there a question of whether Howard will go into space, or is that clear?
I think there’s a question at every point. But by the time the episode starts, it’s pretty clear he’s going. One of the great things about this is when you go up in a Soyuz [Russian space capsule], it’s a three-person craft. It’s always a Russian cosmonaut who’s the pilot, and then the other two might be an astronaut and a cosmonaut or two American astronauts. So the other American astronaut going up in the Soyuz is Mike Massimino, who is a real astronaut, playing himself. Which is pretty awesome.

Mike Massimino is the real-life veteran of two Space Shuttle flights. He was the guy who fixed the Hubble telescope. When you see our Soyuz launch, it required that Mike get into his spacesuit again. We have authentic Russian spacesuits we’re using. Getting in spacesuits is complicated. You need guys to help you get in them – they’re big, bulky things. And Mike was saying it was exactly how it was when he was getting ready to go up on the Space Shuttle. We used our green room as a dressing room, so I said, “Yeah, but you were in some kind of fancy, secure facility.” He said, “No, it pretty much looks like this.”

So weird!
It’s so weird, isn’t it? That’s a personal, great wonderful joy that a real-life astronaut, Mike Massimino, plays himself as the third astronaut going up in the Soyuz capsule with Wolowitz.

Was there a field trip to NASA?
NASA’s worked very closely with us on this. They have been a great source in answering the craziest questions. They’ve been at ready to provide anything we needed. They’ve been an amazing partner in developing this story line.

Was one of the questions “Could someone like Wolowitz actually ever go up in space?”
That was the first question, and the answer was, very quickly, “Yes, absolutely.” We weren’t going to do the story if it wasn’t plausible. Over the years, a number of people have gone up into space who went up because they were traveling with a piece of equipment that they were the expert in. That’s why Wolowitz is going up. He designed a telescope, and someone from his team had to go up to deploy it on the International Space Station. The job is payload specialist. These are people who go for an abbreviated version of full astronaut training, and then go up with a full piece of equipment.

Did Simon have to do any training?
Simon didn’t. Although working in a spacesuit was a little tricky. We depicted it on the show, but he didn’t have to do anything.

For last season’s finale, you had that terrific cliffhanger with Penny and Raj. Can we expect any similar kind of cliffhanger for this finale?
It’s not that kind of cliffhanger. I don’t want to call it a cliffhanger. I’m going to hold them close to the vest, but the end of the show provides three really amazing final moments. Not technically cliffhangers, but cliffhanger adjacent.

Are they all Howard related?
His actions cause all of them. But he’s not involved in all of them.

The last three episodes have been very Howard-centric.
Well, look, these stories were at some point going to come to a head, and we had often mused about having them come to a head simultaneously. So that’s what we did. Everybody is very much involved in these stories. But, yeah, there’s strong Wolowitz and Bernadette stories going on.

There are two other stories – the Sheldon/Amy one, and the Penny/Leonard one.
Those two relationship stories play a part of [the finale]. Both of those couples experience some stuff.

Good stuff, bad stuff, tricky stuff?
Tricky stuff.

Do you think Sheldon and Amy will ever make it to the bedroom?
I have no idea. Here’s the thing that we often talk about in the writers’ room. Sheldon is so stubborn, and yet somehow Amy seems to manage these incremental progressions in their relationship that he seems to accept. It always kind of baffles us when he does it.

She’s proven herself to be equal to the task.
She’s a worthy foe, isn’t she? When she wants something from him, she’s found ways to get it.

Finally, is there a cryptic clue you could give me about season 6?
Not all the characters will be in California when it begins.